The invention relates to component placement.
In general, one goal of electronic equipment manufacturers is to run production lines as quickly and efficiently as possible. To this end, manufacturers extensively use electronic automation to design and produce electronic assemblies. For example, printed circuit boards typically are assembled by "pick-and-place" machines that automatically select an electronic component for placement on a board, properly align the component and the board, and place the component on the board. These machines manufacture printed circuit boards much faster than human workers can.
Referring to FIG. 1A, one type of pick-and-place system often used in industry is a rotating turret-style system 20, such as the CP-series machines produced and sold by Fuji Manufacturing Company. In the turret-style system 20, a rotating turret 22 uses suction arms 24 to pick components 26 from a component table 28 and to place them on a circuit board 30 mounted onto an x,y-table 32. The turret 22 has several arms 24 so that it may pick one component from the component table 28 while it places another component onto the circuit board 30.
Referring also to FIG. 1B, the component table 28 holds reels 34 of tape 36 onto which the components 26 are mounted. When a turret arm 24 picks a component, the component table 28 rotates the reel 34 to expose the next component. The component table 28 moves in the x-direction so that after the system 20 has placed all of the components on one reel, the table 28 may move the next reel into position.
The x,y-table 32 properly positions the printed circuit board to receive components by moving the board in the x-, y-, and z-directions. In most situations, a complex optimization algorithm is used to attempt to minimize the x-, y-, and z-direction movement of the x,y-table 32 and the x-direction movement of the component table 28 while maximizing the rotational speed of the turret 22. Conventional optimization algorithms treat each component type as an individual entity, although most turret-style machines can pick components from any one of three adjacent component reels 34 without any significant reduction in placement speed. The turret 22, component table 28, and x,y-table 32 are controlled by one or more controllers 33 under the direction of a placement program generated by the optimization algorithm.
Referring to FIG. 2, a "shortest path optimization" algorithm is commonly used for component placement. The typical shortest path algorithm determines, for each type of component P, Q on a printed circuit board 38, the order in which the components should be placed to minimize the length of the placement path 40. The algorithm generally begins with the component type P that occurs most frequently on the board 38, then proceeds to the next most common component type Q. The shortest path calculation for the less common component type Q begins at the end 42 of the placement path 40 for the more common type P.